Antifog polyester lidding film for cpet trays

ABSTRACT

The present disclosure is directed to peelable, heat-sealable lidding films for containers of diverse polymer compositions storing various products such as foodstuffs and pharmaceuticals. The lidding films disclosed herein can be heat-sealed to crystalline polyester trays (CPET), easily peeled, and contain improved antifogging performance by incorporating a non-migratory antifogging additive into the heat sealable layer of the film without deteriorating seal strengths.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/476,413, filed Mar. 31, 2017, the entire contents of which isincorporated herein by reference.

FIELD OF THE DISCLOSURE

This disclosure relates to antifog polyester lidding films. Moreparticularly, this disclosure relates to heat-sealable antifog polyesterlidding films for crystalline polyester trays (CPET).

BACKGROUND OF THE DISCLOSURE

Sealed containers with food products such as pastas, salads, wraps,sandwiches, and fruit can provide a quick and convenient meal toconsumers who crave something freshly made. As more and moreready-to-eat meals are available at grocery stores, consumers areoverwhelmed with choices and frequently rely on product appearance inchoosing their food. Many of these meals are packaged in plastic trayswith sealed lids made out of highly transparent, flexible films.However, if the food product contains high amounts of water, the watercan bead up on the lidding film in hot or cold environments. This cancreate a foggy appearance that reduces the visibility of the product tothe consumer which, in turn, may decrease the consumer's probability ofbuying it.

In addition, many lidding films focus on being used as lidding foramorphous polyester trays (APET). However, this type of tray is notovenable and therefore limited to cold or refrigerated onlyapplications.

SUMMARY OF THE DISCLOSURE

Disclosed herein are peelable, heat-sealable lidding films forcontainers of diverse polymer compositions storing various products suchas foodstuffs and pharmaceuticals. Many trays or food containers areprepared and filled in-house (e.g., at the grocery store). These trayscan have a lip extending on the top of the tray for a flexible film tobe sealed using a manual sealer with little to no contamination from thefood on the lip. This film can be embedded with antifogging propertiesthat allow the water condensation droplets to wet-out on the surface inorder to maintain clarity for the consumer. One approach to embed theantifogging properties into the lidding film is to solution-coat anantifogging agent onto the sealable film. Most coatings used to createantifogging performance are solvent-based which can evaporate intovolatile organic compounds (VOCs) which are the increasing focus of airemissions and air quality legislation. Another approach is to impart amigratory additive into the outer layer of the film that will migrateand “bloom” to the surface. The additive is polar and helps thecondensation wet-out into a clear layer that does not hinder theproduct's appearance. However, many times the polar molecules that bloomto the surface can impact seal strength and decrease it to an unwantedlevel.

Applicants have discovered a dual ovenable lidding film that can beheat-sealed to crystalline polyester trays (CPET), easily peeled, andcontains improved antifogging performance by incorporating anon-migratory antifogging additive into the heat sealable layer of thefilm without deteriorating seal strengths. Specifically, the liddingfilms disclosed herein can provide clarity for a product that is keptcold before purchase and can be used when heating the product either ina microwave or oven.

In some embodiments, a lidding film includes a biaxially orientedpolyester-based base film and an extrusion-coated heat seal structure ona side of the base film, wherein the heat seal structure includes a skinlayer including 0.2-5.5 wt % non-migratory antifog active ingredient and70-99 wt % ethylene vinyl acetate (EVA). In some embodiments, thenon-migratory antifog active ingredient includes a non-ionic surfactantand a salt of organic sulfonic acid. In some embodiments, the weightratio of the non-ionic surfactant to the salt of organic sulfonic acidis 20/80-99/1. In some embodiments, the skin layer includes apolyethylene carrier resin for the non-migratory antifog activeingredient. In some embodiments, the non-migratory antifog activeingredient includes 10-25 wt % of the combination of non-migratoryantifog active ingredient and polyethylene carrier resin in the skinlayer. In some embodiments, the polyester-based base film includes acrystalline polyester base layer and an amorphous polyester skin layer.In some embodiments, the extrusion-coated heat seal structure is on aside of the amorphous polyester skin layer opposite the crystallinepolyester base layer. In some embodiments, the crystalline polyesterbase layer includes a polyester resin with an intrinsic viscosity of0.5-0.9 dl/g. In some embodiments, the crystalline polyester base layerincludes polyethylene terephthalate. In some embodiments, the amorphouspolyester skin layer includes at least one of isophthalate modifiedcopolyesters, sebacic acid modified copolyesters, diethyleneglycolmodified copolyesters, triethyleneglycol modified copolyesters, orcyclohexanedimethanol modified copolyesters. In some embodiments, aprimer layer is between the amorphous polyester skin layer and the heatseal structure. In some embodiments, a primer layer is between thepolyester-based base film and the extrusion-coated heat seal structure.In some embodiments, the polyester-based base film includes 0.1-0.4 wt %antiblock or slip additives. In some embodiments, the heat sealstructure includes a core layer including EVA on a side of the skinlayer. In some embodiments, the heat seal structure includes a tie layerincluding low density polyethylene (LDPE) on a side of the core layeropposite the skin layer. In some embodiments, a primer layer is betweenthe tie layer and the base film. In some embodiments, the lidding filmhas an antifog ranking of at least 6. In some embodiments, the liddingfilm has a seal strength to crystalline polyester trays of 500-2500gf/in. In some embodiments, a lidding film includes a biaxially orientedpolyester-base film including a crystalline polyester base layer and anamorphous polyester skin layer and an extrusion-coated heat sealstructure on a side of the base film, wherein the heat seal structureincludes: a tie layer including low density polyethylene (LDPE) on aside of the amorphous polyester skin layer opposite the crystallinepolyester base layer; a core layer including EVA on a side of the tielayer opposite the amorphous polyester skin layer; and a skin layerincluding 0.2-5.5 wt % non-migratory antifog active ingredient and 70-99wt % ethylene vinyl acetate on a side of the core layer opposite the tielayer. In some embodiments, a primer layer is between the amorphouspolyester skin layer and the tie layer.

In some embodiments, a method of forming a lidding film includesbiaxially orienting a polyester-based base film and extrusion coating aheat seal structure including a skin layer including 0.2-5.5 wt %non-migratory antifog active ingredient and 70-99 wt % ethylene vinylacetate (EVA) on a side of the polyester-based base film. In someembodiments, the non-migratory antifog active ingredient includes anon-ionic surfactant and a salt of organic sulfonic acid. In someembodiments, the weight ratio of the non-ionic surfactant to the salt oforganic sulfonic acid is 20/80-99/1. In some embodiments, the skin layerincludes a polyethylene carrier resin for the non-migratory antifogactive ingredient. In some embodiments, the non-migratory antifog activeingredient includes 10-25 wt % of the combination of non-migratoryantifog active ingredient and polyethylene carrier resin in the skinlayer. In some embodiments, the method includes co-extruding acrystalline polyester base layer and an amorphous polyester skin layerto form the polyester-based base film. In some embodiments, the heatseal structure is extrusion coated on a side of the amorphous polyesterskin layer opposite the crystalline polyester base layer. In someembodiments, the method includes solution coating a primer layer on aside of the polyester-based base film, wherein the extrusion-coated skinlayer is on a side of the primer layer opposite the polyester-based basefilm. In some embodiments, the solution coating includes gravure rollcoating. In some embodiments, the method includes corona treating theskin layer. In some embodiments, the lidding film has an antifog rankingof at least 6. In some embodiments, the lidding film has a seal strengthto crystalline polyester trays of 500-2500 gf/in. In some embodiments, amethod of forming a lidding film includes co-extruding a crystallinepolyester base layer and an amorphous polyester skin layer to form apolyester-based base film; biaxially orienting the polyester-based basefilm; solution coating a primer layer including polyethylenimine on aside of the amorphous polyester skin layer opposite the crystallinepolyester base layer; extrusion coating a tie layer including LDPE on aside of the primer layer opposite the amorphous polyester skin layer;extrusion coating a core layer including EVA on a side of the tie layeropposite the primer layer; and extrusion coating a skin layer including0.2-5.5 wt % non-migratory antifog active ingredient and 70-99 wt %ethylene vinyl acetate (EVA) on a side of core layer opposite the tielayer.

Reference to “about” a value or parameter herein includes (anddescribes) variations that are directed to that value or parameter perse. For example, description referring to “about X” includes descriptionof “X”. In addition, reference to phrases “less than”, “greater than”,“at most”, “at least”, “less than or equal to”, “greater than or equalto”, or other similar phrases followed by a string of values orparameters is meant to apply the phrase to each value or parameter inthe string of values or parameters. For example, a statement that thelayer has less than about 20 wt %, about 15 wt %, or about 10 wt % EVA,is meant to mean that the weight percentage of EVA in the layer can beless than about 20 wt %, less than about 15 wt %, or less than about 10wt %.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It is also to be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It is further to beunderstood that the terms “includes”, “including,” “comprises,” and/or“comprising,” when used herein, specify the presence of stated features,integers, steps, operations, elements, components, and/or units but donot preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, units, and/or groupsthereof.

Additional advantages will be readily apparent to those skilled in theart from the following detailed description. The examples anddescriptions herein are to be regarded as illustrative in nature and notrestrictive.

BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments are described with reference to the accompanyingfigures, in which:

FIG. 1 illustrates an example of an embodiment of a sealable liddingfilm disclosed herein.

FIG. 2A is the picture of Example 1's antifogging performance at 120minutes.

FIG. 2B is the picture of Example 2's antifogging performance at 120minutes.

FIG. 2C is the picture of Comparative Example 1's antifoggingperformance at 120 minutes.

FIG. 2D is the picture of Comparative Example 2's antifoggingperformance at 120 minutes.

FIG. 2E is the picture of Comparative Example 3's antifoggingperformance at 120 minutes.

FIG. 2F is the picture of Comparative Example 4's antifoggingperformance at 120 minutes.

FIG. 2G is the picture of Comparative Example 5's antifoggingperformance at 120 minutes.

DETAILED DESCRIPTION OF THE DISCLOSURE

Disclosed herein are antifogging lidding films for crystalline polyester(“CPET”) containers used in packaging goods containing moisture, such asfruits, vegetables, and prepared foods. The antifogging lidding filmsdisclosed herein can be heat-sealed to crystalline polyester trays(CPET), easily peeled, and contain improved antifogging performance byincorporating a non-migratory antifogging additive into the heatsealable layer of the film without deteriorating seal strengths. Thelidding films disclosed herein can provide clarity for a product that iskept cold before purchase and can be used when heating the producteither in a microwave or oven. Specifically, the antifogging liddingfilms can include a biaxially oriented polyester film extrusion-coatedwith a heat-sealable layer that has anti-fog properties obtained byincorporating a non-migratory antifogging additive.

FIG. 1 provides an example of an embodiment of a sealable lidding filmdisclosed herein. The sealable lidding film can include a base film. Asshown in FIG. 1, sealable liddingfilm 1 includes base film 10. The basefilm can be a mono-layer or multi-layer film. In some embodiments, thebase film can include two layers as shown in FIG. 1. The base film canprovide structural integrity of the sealable lidding film and cansupport other layers of the sealable lidding film.

The base film can be a mono-axially or a biaxially-oriented film.Biaxial orientation may be sequential or simultaneous by known methods.In addition, the base film can be a polyester-based film. For example,the base film can include polyethylene terephthalate (PET). In someembodiments, the base film is a biaxially-oriented polyethyleneterephthalate (BOPET) film. In some embodiments, the thickness of thebase film is 9-23 microns.

Typical polyester resins used in the base film can include, but are notlimited to: homopolyesters or copolyesters of polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polyethyleneterephthalate-co-isophthalate copolymer, polyethyleneterephthalate-co-naphthalate copolymer, polycyclohexylene terephthalate,polyethylene-co-cyclohexylene terephthalate, polyether-ester blockcopolymer, ethylene glycol or terephthalic acid-based polyesterhomopolymers and copolymers, and combinations thereof In someembodiments, the polyester comprises poly(ethylene terephthalate) repeatunits. The polyester in the base film can comprise about 70-99.9 wt %.In some embodiments, the base film can be a commercially availablepolyester film such as Toray Plastics (America), Inc.'s Lumirror™ PA10.

In some embodiments, the base film is a two-layer film including a firstlayer on a side of a second layer. In some embodiments, the two-layerbase film can be a first layer coextruded with a second layer. In someembodiments, the base film can include a base layer and/or a skin layer.For example, FIG. 1 includes base layer 10 a and skin layer 10 b of basefilm 10. The base layer and the skin layer of the base film can includeany of the polyesters described above. In some embodiments, the skinlayer of the base film can be an amorphous polyester skin layer. Theamorphous polyester skin layer can help promote adequate adhesion of theheat seal structure to the base film. In some embodiments, the baselayer of the base film can be a crystalline polyester layer.

The term “crystalline polyester” can refer to a polyester that hasdeveloped at least partial crystallinity during the orientation andheat-setting steps of the film-making process. Crystallinity can involvea regular repeating arrangement of the molecules. To produce a crystal,the polymer chains can be capable of packing closely together in aregular, parallel array. The formation of crystals can require polymerchain mobility. Once a certain degree of crystallinity is attained(which depends on the temperature at which crystallization is takingplace) further mobility can be restricted so a fraction of the polymerremains in a non-crystalline state (“amorphous”). Thus the term “degreeof crystallinity” can reflect the relative amount of crystalline regionsand amorphous regions.

The crystalline polyester layer can be a high crystalline polyesterlayer. The high crystalline polyester layer can include high intrinsicviscosity (IV) homopolyesters such as PET, PBT, or PEN, or copolymers orblends thereof. In some embodiments, the crystalline polyester layer caninclude a polyester resin with an intrinsic viscosity greater than about0.4 dl/g, about 0.45 dl/g, about 0.5 dl/g, about 0.55 dl/g, about 0.6dl/g, or about 0.65 dl/g.

In some embodiments, the crystalline polyester layer includespolyethylene terephthalate. In some embodiments, the crystallinepolyester layer can include a polyester resin with an intrinsicviscosity ranging between about 0.45-0.95 dl/g, about 0.5-0.9 dl/g,about 0.55-0.9 dl/g, or about 0.6-0.85 dl/g. In some embodiments, thecrystalline polyester layer can include a polyester resin with a meltingpoint of about 245-270° C., about 250-265° C., or about 255-260° C. Insome embodiments, the crystalline polyester layer can include apolyester resin with a heat of fusion of about 20-60 J/g, about 25-55J/g, or about 30-46 J/g. In some embodiments, the crystalline polyesterlayer can include a polyester resin with a density of about 1-2 g/cm³,about 1.2-1.6 g/cm³, about 1.3-1.5 g/cm³, or about 1.4 g/cm³.

Crystallinity can be defined as the weight fraction of materialproducing a crystal melting endotherm when measured using a differentialscanning calorimeter. For a high crystalline polyester, an exothermicpeak in the melt range of 220° C. to 290° C. can be observed. Highcrystallinity can therefore be defined as the ratio of the heat capacityof material melting in the range of 220° C. to 290° C. versus the totalpotential heat capacity for the entire material present if it were allto crystallize (e.g. 121 J/g). A crystallinity value of greater thanabout 35% weight fraction is considered high crystallinity.

The crystalline polyester layer can further include other additives suchas antiblock and/or slip additives. The additives can typically be solidparticles dispersed within the layer effectively to produce a lowcoefficient of friction on the exposed surface of the layer. This lowcoefficient of friction can help the film to move smoothly through thefilm formation, stretching, and/or wind-up operations. Without suchantiblocking and/or slip additives, the outer surfaces can be more tackyand can likely cause the film being fabricated to stick to itself and toprocessing equipment causing excessive production waste and lowproductivity.

The antiblock and/or slip additives can be added to the base film, baselayer of the base film, and/or skin layer of the base film in an amountof about 0.01-0.5 wt %, about 0.03-0.4 wt %, or about 0.1-0.4 wt % ofthe layer. Examples of antiblock and/or slip additives that may be usedfor polyester film applications can include amorphous silica particleswith mean particle size diameters in the range of about 0.05-0.1 μm atconcentrations of 0.1-0.4 wt % the film or layer; calcium carbonateparticles with a medium particle size of 0.3-1.2 μm at concentrations of0.03-0.2 wt % the film or layer; and precipitated alumina particles ofsub-micron sizes with an average particle sizeof about 0.1 μm atconcentrations of 0.1-0.4 wt % of the layer. Additional examples includeinorganic particles, aluminum oxide, magnesium oxide, titanium oxide,such complex oxides as kaolin, talc, and montmorillonite, suchcarbonates as calcium carbonate and barium carbonate, such sulfates ascalcium sulfate and barium sulfate, such titanates as barium titanateand potassium titanate, and such phosphates as tribasic calciumphosphate, dibasic calcium phosphate, and monobasic calcium phosphate,or combinations thereof. Two or more of these may be used together toachieve a specific objective. As examples of organic particles, vinylmaterials such as polystyrene, crosslinked polystyrene, crosslinkedstyrene-acrylic polymers, crosslinked acrylic polymers, crosslinkedstyrene-methacrylic polymers, and crosslinked methacrylic polymers, aswell as such other materials as benzoguanamine formaldehyde, silicone,and polytetrafluoroethylene may be used or contemplated in the base filmor layers of the base film. One way to incorporate the aforementionedantiblock particles can be via masterbatch addition. In such anembodiment, a high crystalline polyester layer can be produced byextruding a pellet-to-pellet mix of unfilled polyester pellet andmasterbatch polyester pellet (additive concentrate).

In some embodiments, the amorphous polyester skin layer can includeabout 70-100% of any of the following or combinations of the following:isophthalate modified copolyesters, sebacic acid modified copolyesters,diethyleneglycol modified copolyesters, triethyleneglycol modifiedcopolyesters, and/or cyclohexanedimethanol modified copolyesters. Insome embodiments, copolyesters in the amorphous polyester skin layerhave a low melting or amorphous aromatic copolyester (such as one basedon terephthalate/isophthalate copolymer with ethylene glycol or acopolyester made from a combination of terephthalic acid, ethyleneglycol, and cyclohexyldimethanol). In some embodiments, the amorphouspolyester skin layer can include a copolymer with about 15-20 wt %isophthalate and about 80-85 wt % terephthalate polyesters with ethyleneglycol.

The base film can produced by melt extrusion (if monolayer) orco-extrusion (if comprised by two or more layers, e.g., base and skinlayer as described above). In addition, the base film can be stretchedin one or two orthogonal directions, i.e., for mono- or biaxialorientation. This orientation process can provide greater strength forthe base film, and thus also for the overall film. The orientation alsocan permit the film to be produced to a thinner cross-section dimension.

A heat seal structure can be applied to one side of the base film. Forexample, heat seal structure 12 is applied to one side of basefilm 10 inFIG. 1. In some embodiments, the heat seal structure can be applied toone side of the skin layer of the base film that is opposite the baselayer of the base film. In some embodiments, a primer layer can beapplied to one side of the base film. In some embodiments, the primerlayer can be added by a solution coating method, such as gravure rollcoating. In some embodiments, the primer layer comprisespolyethylenimine, ethylene acrylic acid copolymer, ethylene methylacrylate, urethane, or combinations thereof. In some embodiments, thedry coat weight of the primer layer can be up to about 0.03 pounds perream. In some embodiments, the dry coat weight of the primer layer canbe about 0.005-0.02, about 0.0075-0.015, about 0.0075-0.0125, or about0.01 pounds per ream. The primer layer can be between the base film andthe (extrusion-coated) heat seal structure to help ensure strongadhesion of the heat seal structure to the base film. In someembodiments, the primer layer can be formed using MICA A-131-X. The heatseal structure can be applied to the side of the primer layer facingaway from the base film. Such a configuration is shown in FIG. 1 withbase film 10, primer layer 11, and heat seal structure 12. In someembodiments, the heat seal structure can be applied to one side of thebase film, with or subsequent to, applying the primer layer. In someembodiments, the heat seal structure is extrusion-coated on to the basefilm. In some embodiments, the heat seal structure is extrusion-coatedon the base film, with or subsequent to, applying the primer layer. Theextrusion-coating can be applied under conditions that prevent excessiveheating which could degrade the heat-seal polymers.

The heat seal structure can provide the film with the ability to beheat-sealed to itself or to other films, sheets, or trays made fromcrystallized polyethylene terephthalate (CPET), amorphous polyethyleneterephthalate (APET), foil, PET-coated paperboard, PE-coated paperboard,PVC, glass, polypropylenes or polyethylenes, polylactic acid,polystyrenes (PS), or other polyolefins at temperatures ranging from 50to 200° C. The heat seal structure can be formulated to provide either adestructive bond, or preferably a peelable bond to the other tray orcontainer material. In some embodiments, the seal range for the heatseal structure (to itself or to other substrates) is between 300 gm/into 3,000 gm/in (based on sealing at 275° F., 30 psia (jaw pressure), 0.5seconds dwell). In some embodiments, the heat seal structure's thicknessis between 25 and 95 μm or 47 to 77 μm.

The heat seal structure can include a thermally activatable adhesivecomposition, typically referred to as hot-melt adhesive resin. The heatseal structure can provide the film with the ability to be heat-sealedto itself, other films, sheets, trays, or other substrates. Thesesubstrates, films, sheets, or trays can be made from crystallizedpolyethylene terephthalate (CPET), amorphous polyethylene terephthalate(APET), foil, polyethylene terephthalate-coated (PET) paperboard,polyethylene (PE)-coated paperboard, PVC, glass, aliphatic olefinpolymers such as polypropylene and polyethylene, and other polyolefinssuch as polystyrene (PS) and the like.

The hot-melt, thermally activated adhesive composition can includepolymers selected from polyethylene homopolymers such as low densitypolyethylene (LDPE) and medium density polyethylene (MDPE); copolymersof ethylene and at least one ethylenically unsaturated comonomerselected from vinyl acetate, acrylic acid, C₁-C₄ alky ester of acrylicacid, C₁-C₄ alkyl ester of a C₁-C₄ alkylacrylic acid, and cyclic olefincopolymers and blends thereof. Representative examples of copolymer ofethylene and ethylenically unsaturated comonomer includeethylene/vinylacetate copolymer (EVA), ethylene/acrylic acid copolymer(EAA) ethylene/methyl acrylate copolymer (EMA),ethylene/methylmethacrylate copolymer (EMMA), ethylene/methylacrylate/acrylic acid copolymer (EMAAA), ethylene/methylacrylate/methacrylic acid copolymer (EMAMAA), and ethylene/butylacrylate/acrylic acid copolymer (EBAAA).

The heat seal structure can be a monolayer or can be multilayered. Theheat seal structure can be deposited by extrusion-coating on the primerlayer or on the base film. In some embodiments, the heat seal structurecan include two or three sublayers. Each of these sublayers can also beextrusion-coated either individually or together on the primer layer oron the base film. For example, FIG. 1 illustrates sublayer 12 a,sublayer 12 b, and sublayer 12 c of heat seal structure 12.

The first sealant sublayer (i.e., the sublayer closest to the base film)can act as a tie layer to the base film (with or without primer layer inbetween). The first sealant sublayer can include low densitypolyethylene (LDPE). In some embodiments, the first sealant layer can bea conventional high-pressure autoclave-polymerized LDPE resin such as,but not limited to, Marflex® 1017 and Marflex® 1019 (Chevron Philips)and Dow LDPE 722 (Dow Chemical Co.). These materials can becharacterized by high melt strength and are known for excellentextrusion-coating performance, stability and high melt strength, and lowdegree of “necking”. Another advantage of these LDPE materials can bethe high bonding strength to the amorphous or low crystallinity layer ofthe base film. This advantage can be achieved by the surface oxidationof the extrusion-coated layer melt curtain emerging from the die.Surface oxidation of the extrusion-coating can be controlled by melttemperature and the amount of time within the air gap as determined bythe line speed and the distance between the die exit and the contactwith the base film. Additionally, an optional ozone-generating unit cansupply ozone gas within this gap to aid in oxidation of the polymersurfaces of the heat seal structure and increase processing window (suchas lower extrusion temperatures and/or smaller amount of residence timewithin the air gap). Using these LDPE materials in the first sealantsublayer can provide a good extrusion-coating base upon which the secondand/or third sealant sublayers are coextruded with the first sealantsublayer. In some embodiments, the thickness of the first sealant layercan be about 2.5-7.5 microns or 5-6.25 microns.

The second sealant sublayer (i.e., the sublayer on a side of the firstsealant sublayer opposite the base film) can act as a core layer of theheat seal structure. The second sealant sublayer can include EVA. EVA isa copolymer of ethylene and vinyl acetate (the vinyl acetate percentageranging between 12 -28 mole %, preferably 19 mole % of the polymer) thatcan provide a suitable heat sealable material due to its low meltingtemperature. In some embodiments, the thickness of the second sealantlayer can be about 2.5-12.5 microns or 5-10 microns.

The third sealant sublayer (i.e., the sublayer on a side of the secondsealant sublayer opposite the first sealant sublayer) can act as a skinlayer of the heat seal structure. In some embodiments, the thickness ofthe third sealant layer can be about 1.25-3.75 microns or 1.75-3microns. The third sealant layer can include an antifog additive. Insome embodiments, the antifog additive can be in the form of amasterbatch in a polyethylene carrier resin.

Typically, an antifog additive's active ingredients can be amphiphilicmolecules with polar and non-polar segments. The non-polar segment hasan affinity for the polymer matrix, while the polar segment does not.This partial incompatibility can drive migration of the antifog additiveto the surface of the heat seal structure (more precisely, in the caseof lidding film, the inner surface of the heat seal structure, i.e. theside facing the product, upon which the water droplets are being formedfrom moisture condensation). The antifog additive can act as asurface-active agent, resulting in the heat seal structure's outersurface becoming more polar (polymer surface energy increases); theantifog can partially dissolve in the water droplets (decreases surfacetension of water) and thus, can allow the water droplets to spread outas a thin film instead of discrete droplets, helping to ensuretransparency and a clearer view of the package contents by the consumer.

One problem with conventional antifog additive's active ingredients isthe continued migration to both the exposed film surface facing theproduct and to the opposite direction towards the underlying layers andbase film. Migration towards the exposed surface can result in theantifog additive's active ingredients being slowly depleted and also toaffecting seal strength by weakening the seal strength. Migrationtowards the opposite direction can result in the antifog additive'sactive ingredients eventually reaching the extrusion-coating interfacewith the base film (or primer layer) and potentially causingdelamination from the base film. For the most effective performance, theadditive's active ingredients can be one that undergoes little or nomigration. The antifog additive's active ingredients that findthemselves exposed to the surface after extrusion-coating andfilm-making (and also a small amount that is allowed to migrateimmediately after the film is made) can be permanently anchored to theexposed surface and provide the necessary surface activation but may notleach out. Also they may not migrate to the opposite direction causingpotential delamination issues with the base film. Such additive's activeingredients in that category can be esters of aliphatic alcohols,polyethers, polyhydric alcohols, esters of polyhydric aliphaticalcohols, polyethoxylated aromatic alcohols, nonionic ethoxylates, andhydrophilic fatty acid esters. Specific antifog additive's activeingredients that may be used include polyoxyethylene, sorbitanmonostearate, polyoxyethylene sorbitan monolaurate, polyoxyethylenemonopalmitate, polyoxyethylene sorbitan tristearate, polyoxyethylenesorbitan trioleate, poly(oxypropylene), polyethoxylated fatty alcohols,polyoxyethylated 4-nonylphenol, polyhydric alcohol, propylene diol,propylene triol, and ethylene diol, monoglyceride esters of vegetableoil or animal fat, mono- and/or diglycerides such as glycerolmono-stearate.

Accordingly, the active ingredient of the antifog additive in thelidding films disclosed herein can be non-migratory. The non-migratoryantifog active ingredient can eliminate or decrease the impact on sealstrength or seal characteristics when compared to other antifog activeingredients. The non-migratory antifog active ingredient can include acombination of: (A) a non-ionic surfactant; and (B) a salt of organicsulfonic acid. Without being bound by any theory, it is believed thatthe combination of a non-ionic surfactant with a salt of organicsulfonic acid can provide the non-migratory properties. Examples ofnon-ionic surfactants and salt of organic sulfonic acid can be found inU.S. Pat. No. 6,958,193 and U.S. Publication No. 2005/0136275 which areherein incorporated by reference in their entirety. The weight ratio ofthe non-ionic surfactant to the salt of organic sulfonic acid can beabout 10/100-100/100, about 20/80-99/1, about 50/50-90/10, or about60/40-80/20. The non-migratory active ingredient in the antifog additivemasterbatch can be less than or equal to about 20 wt % the masterbatch(remainder polyethylene carrier resin). In some embodiments, thenon-migratory active ingredient in the antifog additive masterbatch isabout 5-30wt %, about 10-25wt %, about 15-20 wt %, about 17-19 wt %, orabout 18 wt % the masterbatch. In some embodiments, the third sealantlayer can include about 0.05-6 wt %, about 0.2-5.5 wt %, about 1-4.5 wt%, about 1.5-5 wt %, about 1.5-4.5 wt %, about 1.8-3.5, or about 1.8-2.7wt % the non-migratory active ingredient in the antifog additive. Insome embodiments, the third sealant layer can include EVA. In someembodiments, the third sealant layer can include about 1-30 wt %, about5-25 wt %, about 10-20 wt %, or about 10-15 wt % the antifog additivemasterbatch. In some embodiments, the third sealant layer can includeabout 70-99 wt %, about 75-95 wt %, about 80-90 wt %, or about 85-90EVA.

Specific examples of a non-ionic surfactant include, but are notlimited, diglycerol monostearate; triglycerol monolaurate; sorbitanmonostearate; myristyl diethanol amide; glycerol monostearate; mixtureof glycerol monostearate and sorbitan monostearate at weight ratio of50/50; lauryl diethanol amine; mixture of glycerol monostearate andmyristyl diethanol amide at weight ratio of 50/50; mixture of glycerolmonostearate and lauryl diethanol amine at weight ratio of 50/50;diglycerol monolaurate (melting point=20° C.); mixture of diglycerolmonostearate (melting point=55° C.) and diglycerol monooleate (meltingpoint=2° C.) at weight ratio of 65/35; mixture of diglycerolmonostearate (melting point=55 ° C.) and glycerol monooleate (meltingpoint=12° C.) at weight ratio of 50/50; mixture of diglycerolmonolaurate (melting point=20° C.) and glycerol monooleate (meltingpoint=12° C.) at weight ratio of 70/30; mixture of sorbitan monooleate(melting point=8° C.) and glycerol monooleate (melting point=12° C.) atweight ratio of 70/30; mixture of glycerol monooctanate (meltingpoint=35° C.) and diglycerol monolaurate (melting point=20° C.) atweight ratio of 15/85; mixture of glycerol monoerucate (meltingpoint=50° C.) and diglycerol monolaurate (melting point=20° C.) atweight ratio of 10/90; mixture of tetraglycerol monooctanate (meltingpoint=25° C.) and diglycerol monolaurate (melting point=20° C.) atweight ratio of 15/85; mixture of tetraglycerol monoerucate (meltingpoint=50° C.) and diglycerol monolaurate (melting point=20° C.) atweight ratio of 10/90; mixture of glycerol monolaurate (meltingpoint=55° C.) and diglycerol monolaurate (melting point=20° C.) atweight ratio of 10/90; mixture of tetraglycerol monooleate (meltingpoint=25° C.) and diglycerol monolaurate (melting point=20° C.) atweight ratio of 10/90; ethylene oxide adduct of octyl alcohol (averagemolecular weight=450, melting point=5° C.); ethylene oxide adduct ofdocosenyl alcohol (average molecular weight=1200, melting point=50° C.);diglycerol monostearate (melting point=55° C.); sorbitan monostearate(melting point=60° C.); mixture of diglycerol monostearate (meltingpoint=55° C.) and glycerol monostearate (melting point=70° C.) at weightratio of 50/50; mixture of sorbitan monostearate (melting point=60° C.)and glycerol monostearate (melting point=70° C.) at weight ratio of50/50; ethylene oxide adduct of octanic acid (average molecularweight=450, melting point=5° C.); ethylene oxide adduct of docosenicacid (average molecular weight=1200, melting point=50° C.); ethyleneoxide adduct of glycerol monooctanate (average molecular weight=900,melting point=30° C.); diglycerol monooctanate (melting point=-8° C.);ethylene oxide adduct of octadecenyl alcohol (average molecularweight=900, melting point=2° C.); ethylene oxide adduct of dodecanoicacid (average molecular weight=350, melting point=7 C.); ethylene oxideadduct of sorbitan monooleate (average molecular weight=950, meltingpoint=-10° C.); ethylene oxide adduct of glycerol monoerucate (averagemolecular weight=1000, melting point=30° C.); ethylene oxide adduct oftetraglycerol monooctanate (average molecular weight=1200, meltingpoint=25° C.); or ethylene oxide adduct of tetraglycerol monoerucate(average molecular weight=1400, melting point=25° C.).

Specific examples of a salt of organic sulfonic acid include, but arenot limited, sodium myristyl sulfonate; sodium dioctyl sulfo succinate;sodium dodecyl benzene sulfonate; mixture of sodium dioctyl sulfosuccinate and sodium dodecyl benzene sulfonate at weight ratio of 50/50;lithium dibutyl naphthalene sulfonate; potassium.alpha.-(p-nonylphenyl)-.omega.-hydroxypoly (oxyethylene) sulfoacetate(oxyethylene repetition number=3); sodium dodecylsulfonate; sodiumtetradecylsulfonate; sodium pentadecylsulfonate; sodiumHexadecylsulfonate; mixture of sodium tetradecylsulfonate and sodiumpentadecylsulfonate at weight ratio of 50/50; lithium dodecylsulfonate;lithium octadecylsulfonate; potassium dodecylsulfonate; potassiumoctadecylsulfonate; sodium hexylsulfonate; sodium docosylsulfonate;sodium docosylbenzene sulfonate; mixture of potassium diethylnaphthalenesulfonate and potassium docosylbenzene sulfonate at weight ratio of50/50; potassium tetradecylsulfonate; lithium dodecylbenzene sulfonate;potassium 1,2-bis(octyloxycarbonyl)-1-ethane sulfonate; mixture ofsodium dodecylbenzene sulfonate and sodium 1,2-bis(octyloxycarbonyl)-1-ethane sulfonate at weight ratio of 50/50;potassium 1,2-bis (ethyloxycarbonyl)-1-ethane sulfonate; sodium1,2-bis(dodecyloxycarbonyl)-1-ethane sulfonate; mixture of lithium1,2-bis(ethyloxycarbonyl)-1-e-thane sulfonate and lithium 1,2-bis(dodecyloxycarbonyl)-1-ethane sulfonate at weight ratio of 50/50;lithium octylsulfonate; potassium hexylbenzen sulfonate; lithiumdibutylnaphthalene sulfonate; mixture of lithium octylsulfonate andlithium dibutylnaphthalene sulfonate at weight ratio of 50/50; sodiumoctylsulfonate; potassium 1,2-bis(docosyloxycarbonyl)-1-ethanesulfonate; or mixture of lithium octylsulfonate and lithium1,2-bis(docosyloxycarbonyl)-1-ethane sulfonate.

The heat seal structure can be modified by addition of organic orinorganic particulates for various purposes. Representative examples ofsuch additives include amorphous silica, calcium carbonate, clay, talc,diatomaceous earth, cross-linked spherical polydimethylsiloxane,cross-linked spherical organic polymers, or glass beads, or mixtures oftwo or more of these ingredients for antiblocking purposes; slip agentssuch as, but not limited to, a fatty amide: erucamide, stearamide,behenamide, or bisamides (e.g. stearyl-erucamide), silicone oil, and/ormixtures of same; antifog agents such as, but not limited to, glycerolmonostearate; and antistatic agents such as, but not limited to,glycerol monostearate. These additives can be added to the heat sealstructure or any sublayer of the heat seal structure in an amount ofabout 0.01-0.5 wt %, about 0.03-0.4 wt %, or about 0.1-0.4 wt % of thelayer. In some embodiments, the additives can be only in the outermostsublayer of the heat seal structure, i.e., the layer that is furthestfrom the base film. A multilayer heat seal structure can be free ofcertain additives in sub-layers, i.e., those sublayers closer inproximity to the adhesive primer layer or base film; and additives inthe outermost sublayer of the heat seal structure (i.e. the side of theheat seal structure facing the product or product container). Forexample, slip agent particulates can be incorporated into the outermostsublayer of the heat seal structure to reduce blocking of the film andpromote ease of film handling.

The side of the heat seal structure opposite the base film (i.e., theoutermost side of the heat seal structure) can also be treated. In someembodiments, the side of the heat seal structure opposite the base filmcan be modified by an electrical-discharge treatment (such as plasma orcorona) to provide specific seal properties to specific substrates. Insome embodiments, the applied watt density to the side of the heat sealstructure opposite the base film can be in the range of 0.5-5watts/square feet/min. In some embodiments, the third sealant sublayeris the sublayer of the heat seal structure that is treated (e.g., coronatreated or plasma treated).

The heat seal structure can have a thickness that ranges from about 6-24microns or about 12-20 microns. In addition, the normal heat sealparameters for the lidding films disclosed herein can be about 200-400°F., about 275-400° F., or about 300-375° F.

EXAMPLES Raw Materials for Examples

Base Film: Commercial PET polyester film Lumirror® 48G PA10, availablefrom Toray Plastics (America), Inc., having a thickness of 48 gauge (12μm) and an asymmetrical two-layer structure comprising a main layercomprising crystallized PET; and a coextruded skin layer, suitable foradhesion or printing, comprising an amorphous copolyester. In theexamples and comparative examples where this film was employed as thebase film, extrusion-coating of the sealant layer was conducted on thesurface corresponding to the amorphous polyester skin layer.

Seal Layer(s):

Marflex® 1017: Low-density (LDPE) resin produced by Chevron Philips(density 0.917 g/cc, melt index 7 g/10 min, melting point 106° C.).

Mica A-131-X: Polyethyleneimine water-based extrusion primer from Mica™Corporation containing 5% solids with a pH of 10.7.

Ateva® 1943: Ethylene vinyl acetate (“EVA”) resin (18 mole % vinylacetate; density 0.937 g/cc, melt index 30 g/10 min, melting point 85°C.) from Celanese.

Ateva® 2821A: Ethylene vinyl acetate (“EVA”) resin (28 mole % vinylacetate; density 0.948 g/cc, melt index 25 g/10 min, melting point 70°C.) from Celanese.

Takemoto Oil & Fat Co. TRB-002: Antifog masterbatch from Takemoto at anactive ingredient (comprising a non-ionic surfactant and a salt oforganic sulfonic acid) level of less than or equal to 20 wt % in apolyethylene carrier resin.

Mitsui AF 22PE-2700: Antifog formulation in the form of concentrate inpolyethylene resin.

Elecutmaster AB-8200: Antiblock masterbatch from Takemoto Oil & Fat Co.,Ltd., comprising 30 wt % of an antiblock and slip agent with averageparticle size 3-4 μm in polyethylene carrier resin.

Polybatch F20: Antiblock additive masterbatch (active ingredient naturalsilica with an average size of 9 μm, present at 20 wt %) in polyethylenecarrier (melting point 122.5° C.) produced by A. Schulman.

Film Conversion Process for Examples

Extrusion-coating was conducted on an extrusion-coating line within-line corona treatment, gravure roll priming coating station, andozonation as noted in the examples below. The extrusion-coated seallayer was applied as a molten resin curtain onto the base polymeric film(Lumirror™ PA10). The temperature range of this molten resin curtaindepends on the type of resin used but generally was between 175° C. and350° C. This molten curtain was cooled as soon as it contacts thepolymeric film since a chill roll supports the base film. The chill rollis usually kept at temperatures between 50° C. and 20° C.

Example 1

A 48G polyester film was extrusion-coated with 73G of a heat sealstructure, comprising a tie layer, a core layer, and a skin layer asshown in Table 1. The 9G skin sublayer contains 10 wt % of TRB-002.

Example 2

A 48G polyester film was extrusion-coated with 73G of a heat sealstructure, comprising a tie layer, a core layer, and a skin layer asshown in Table 1, the 9G skin sublayer contains 15 wt % of TRB-002.

Comparative Example 1

A 48G polyester film was extrusion-coated with 73G of a heat sealstructure, comprising a tie layer, a core layer, and a skin layer asshown in Table 1.

Comparative Example 2

A 48G polyester film was extrusion-coated with 7G of a heat sealstructure, comprising a tie layer, a core layer, and a skin layer asshown in Table 1.

Comparative Example 3

DuPont's Mylar ® OLAF antifog lidding film.

Comparative Example 4

DuPont's Mylar ® RL42AFT antifog lidding film.

Comparative Example 5

A 48G polyester film was extrusion-coated with 72G of a heat sealstructure, comprising a tie layer, a core layer, and a skin layer asshown in Table 1, the 9G skin sublayer contains 10 wt % AF 22PE producedby Mitsui Plastics.

TABLE 1 Film Layer Structures with Compositions of the Examples ExampleExample 1 Example 2 Composition Composition (wt % as applicable)Thickness (wt % as applicable) Thickness Overall Structure 121.5 G 121.5G (30.9 μm) (30.9 μm) Base Film Lumirror ® PA10 48 G Lumirror ® PA10 48G (12.2 μm) (12.2 μm) Treatment Corona 0.2 W/m² Corona 0.2 W/m² PrimerMica A-131-X 0.01 #/rm  Mica A-131-X 0.01 #/rm  Tie Sealant Layer ofMarflex ® 1017 24.46 G Marflex ® 1017 24.46 G Heat-Sealant StructureLDPE 100% (6.2 μm) LDPE 100% (6.2 μm) Core Sealant Layer of Ateva ® 1943100% 39.22 G Ateva ® 1943 100% 39.22 G Heat-Sealant Structure (10.0 μm)(10.0 μm) Skin Sealant Layer of Ateva ® 1943 87% 9.81 G Ateva ® 1943 72%9.81 G Heat-Sealant Structure Takemoto TRB-002 10% (2.5 μm) TakemotoTRB-002 15% (2.5 μm) Takemoto AB-8200 3% Ateva ® 2821A 10% TakemotoAB-8200 2% Total Heat-Sealant 73.46 G 73.46 G Structure Thickness (18.6μm) (18.6 μm) Example Comparative Example 1 Comparative Example 2Composition Composition (wt % as applicable) Thickness (wt % asapplicable) Thickness Overall Structure 121.5 G 120 G (30.9 μm) (30.5μm) Base Film Lumirror ® PA10 48 G Lumirror ® PA10 48 G (12.2 μm) (12.2μm) Treatment Corona 0.2 W/m² Corona 0.2 W/m² Primer Mica A-131-X 0.01#/rm  Mica A-131-X 0.01 #/rm  Tie Sealant Layer of Marflex ® 1017 24.46G Marflex ® 1017 24 G Heat-Sealant Structure LDPE 100% (6.2 μm) LDPE100% (6.1 μm) Core Sealant Layer of Ateva ® 1943 100% 39.22 G Ateva ®1943 100% 39 G Heat-Sealant Structure (10.0 μm) (9.9 μm) Skin SealantLayer of Ateva ® 1943 97% 9.81 G Ateva ® 1943 87% 9 G Heat-SealantStructure Takemoto AB-8200 3% (2.5 μm) Ateva ® 2821A 10% (2.3 μm)Takemoto AB-8200 3% Total Heat-Sealant 73.46 G 72 G Structure Thickness(18.6 μm) (18.3 μm) Example Comparative Example 5 Composition (wt % asapplicable) Thickness Overall Structure 120 G (30.5 μm) Base FilmLumirror ® PA10 48 G (12.2 μm) Treatment Corona 0.2 W/m² Primer MicaA-131-X 0.01 #/rm  Tie Sealant Layer of Marflex ® 1017 24 G Heat-SealantStructure LDPE 100% (6.1 μm) Core Sealant Layer of Ateva ® 1943 100% 39G Heat-Sealant Structure (9.9 μm) Skin Sealant Layer of Ateva ® 1943 89%9 G Heat-Sealant Structure Mitsui AF 22PE 10% (2.3 μm) A. SchulmanPolybatch F20 1% Total Heat-Sealant 72 G Structure Thickness (18.3 μm)

Thickness of extruded films, coextruded film layers, and extrusioncoated film layers can be expressed in G (film gauge) units. 1 G equals0.01 mil (1 mil= 1/1000 in). The film gauge unit can also be convertedto pm (micrometer or “micron” unit) by multiplying times 0.254 (i.e.1G=0.254 μm).

Thickness (more precisely weight per unit area) of coated primer canexpressed in units of #/rm (pounds per ream). Ream is a unit of surfacearea equal to 3000 ft² (=432,000 in²).

Testing

Antifogging Test: Each example's antifog performance was judged usingToray Plastics (America), Inc.'s antifogging test. Materials needed forthe antifogging test include glass Ball® canning jars with metaltwist-on rims for every sample and a control, the films to be tested,and a camera to document the antifog performance results. Each of thefilms to be tested were cut into 4″ by 4″ squares and the jars werefilled with 300mL of water. The antifog-containing side of the film wasplaced over the jar's mouth, facing downward towards the water, takingcare not to splash any water onto the film. A flat, tight seal of thefilm to the jar was secured using the metal screw-on rims. The jars wereleft at room temperature for an hour, then photographed for the initialtime point signifying start of the test; and placed in a refrigeratorkept at 35 to 45° F. The jars were checked at 15, 30, 60, 120, and 1440minutes, photographed and judged on their antifog performance.Antifogging performance is based on a numerical ranking corresponding todescription of fogging appearance and the scale is shown in Table 2.

TABLE 2 Antifog Performance Ranking Antifog Ranking Description 1 Foggyfine drops 2 Very hazy small drops 3 Hazy medium drops 4 Translucentlarge drops 5 Particularly clear small drops 6 Mostly clear medium drops7 Clear large drops 8 Clear

FIGS. 2A-G contain the pictures of the Examples and the ComparativeExamples' antifogging performance at 120 minutes.

The lidding films disclosed herein have an antifog ranking of at least5, at least 6, or at least 7. In some embodiments, the lidding filmsdisclosed herein have an antifog ranking of 5-8, 6-8, 7-8, or 8.

Seal Strength Testing: As described above, another important attributeof the lidding films disclosed herein are that they have strong seals tocrystalline polyester trays. The examples were sealed using a tabletopSentinel™ sealer (model 12ASL) at 30 psia and 0.5 second dwell, with onesealer jaw (upper) heated and the other sealer jaw (lower) unheated. Arange of temperatures were tested ranging from 225° F. to 375° F. A CPETtray (obtainable from a CPET tray manufacturer or from retail storeshelves and cleaned of product) was used to seal with the antifog film.The bottom of the CPET tray is used for flatness and thicknessuniformity. A piece of CPET tray about 3″×2″ is cut out and aligned witha similarly sized piece of test film, with the heat seal structure sideof the test film against the CPET. This construct was then placed in theSentinel™ sealer jaws and heat-sealed together. The sealed construct wasthen cut into 1″ wide sample strips. The samples were then peeled on anInstron® tensile tester machine with the seal strength and peelcharacteristics noted.

The lidding films disclosed herein have a seal strength to itself orother substrates such as crystalline polyester trays in the range ofabout 500-2,500 gf/in, about 500-2,000 gf/in, about 1,000-2,000 gf/in,about 1,000-1,500 gf/in, about 1,300-2,500 gf/in, about 1,300-2,000gf/in, or about 1,300-1,500 gf/in, measured at 350° F., 30 psia jawpressure, 0.5 seconds dwell.

Table 3 below provides the heat seal strength results of the Examplesand Comparative Examples at 350° F.

TABLE 3 Testing Results of the Films in the Examples Seal Strength PeelAntifog Ranking at 350 F. (gf/in) Characteristics at 120 Minutes Example1 1358 Clean Peel 6 Example 2 1393 Clean Peel 7 Comparative 992 CleanPeel 1 Example 1 Comparative 1200 Clean Peel 1 Example 2 Comparative1296 Clean Peel 4 Example 3 Comparative 945 Clean Peel 5 Example 4Comparative 634 Clean Peel 5 Example 5

As shown in the above Table, the films of Examples 1 and 2 (containing10 and 15 wt %, respectively of Takemoto TRB-002 antifog masterbatchformulation, i.e. 1.8 and 2.7 wt.% respectively of the active ingredientin the layer with heat seal skin layer) have acceptable antifog rankingsvs. either a blank control film (i.e. no antifog present; Comp. Ex. 2)or vs. films containing earlier generations of standard antifogformulations. In addition to the good antifog ratings, excellent sealstrengths and peel characteristics to CPET tray material are maintainedin Examples 1 and 2.

This application discloses several numerical ranges in the text andfigures. The numerical ranges disclosed inherently support any range orvalue within the disclosed numerical ranges, including the endpoints,even though a precise range limitation is not stated verbatim in thespecification because this disclosure can be practiced throughout thedisclosed numerical ranges.

The above description is presented to enable a person skilled in the artto make and use the disclosure, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the disclosure. Thus, this disclosure is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein. Finally,the entire disclosure of the patents and publications referred in thisapplication are hereby incorporated herein by reference.

1. A method of forming a lidding film comprising: biaxially orienting apolyester-based base film; and extrusion coating a heat seal structurecomprising a skin layer comprising 0.2-5.5 wt % non-migratory antifogactive ingredient and 70-99 wt % ethylene vinyl acetate (EVA) on a sideof the polyester-based base film.
 2. The method of claim 1, wherein thenon-migratory antifog active ingredient comprises a non-ionic surfactantand a salt of organic sulfonic acid.
 3. The method of claim 2, whereinthe weight ratio of the non-ionic surfactant to the salt of organicsulfonic acid is 20/80-99/1.
 4. The method of claim 1, wherein the skinlayer comprises a polyethylene carrier resin for the non-migratoryantifog active ingredient.
 5. The method of claim 4, wherein thenon-migratory antifog active ingredient comprises 10-25 wt % of thecombination of non-migratory antifog active ingredient and polyethylenecarrier resin in the skin layer.
 6. The method of claim 1, furthercomprising co-extruding a crystalline polyester base layer and anamorphous polyester skin layer to form the polyester-based base film. 7.The method of claim 6, wherein the heat seal structure is extrusioncoated on a side of the amorphous polyester skin layer opposite thecrystalline polyester base layer.
 8. The method of claim 1, furthercomprising solution coating a primer layer on a side of thepolyester-based base film, wherein the extrusion-coated skin layer is ona side of the primer layer opposite the polyester-based base film. 9.The method of claim 8, wherein the solution coating comprises gravureroll coating.
 10. The method of claim 1, further comprising coronatreating the skin layer.
 11. The method of claim 1, wherein the liddingfilm has an antifog ranking of at least
 6. 12. The method of claim 1,wherein the lidding film has a seal strength to crystalline polyestertrays of 500-2500 gf/in.
 13. A method of forming a lidding filmcomprising: co-extruding a crystalline polyester base layer and anamorphous polyester skin layer to form a polyester-based base film;biaxially orienting the polyester-based base film; solution coating aprimer layer comprising polyethylenimine on a side of the amorphouspolyester skin layer opposite the crystalline polyester base layer;extrusion coating a tie layer comprising LDPE on a side of the primerlayer opposite the amorphous polyester skin layer; extrusion coating acore layer comprising EVA on a side of the tie layer opposite the primerlayer; and extrusion coating a skin layer comprising 0.2-5.5 wt %non-migratory antifog active ingredient and 70-99 wt % ethylene vinylacetate (EVA) on a side of core layer opposite the tie layer.